The present invention relates generally to a system for regenerating emission filters and, more particularly, to such a system for use in a Diesel engine.
Particulate matter such as carbon are contained in the exhaust gases of a Diesel engine, and removal of these particulates typically is accomplished by a particulate filter disposed in an exhaust pipe. Such a particulate filter is formed, for example, from ceramics formed with a number of slots arranged to collect the particulates as exhaust gases flow through in a circuitous fashion. After an extended period of use, conventional particulate filter become clogged and require regeneration.
In the past, there has been proposed a filter regenerating device having an electric heater for burning particulate matter at the inlet of the particulate filter. This prior art device, however, consumes substantial electrical power and can cause discharge of power source batteries.
An improved regeneration system is disclosed in Japanese Patent Application, Laid-Open No. 128912/84. In that system a combustor is arranged at the inlet of a particulate filter, and generates high temperature combustion gases for burning the particulates. Fuel is supplied to the combustor by an injection device and is mixed with air for combustion. However, for fuels such as light oil or gasoline poor in volatility, vaporization is not promoted by mere spray mixing with air so that the fuel often is supplied to the combustor in the form of droplets. Consequently, combustion produces smoke of high concentration in the combustor, further contaminating the particulate filter. To enhance the firing property of fuel in the combustor a back-flow type vaporization cylinder is employed to utilize fully the heat of exhaust gases. However, the vaporization cylinder requires the energy of hot exhaust gases produced during high load operation of the engine, and the particulate filter is not regenerated during low load engine operation.
In the above described system, the combustor is operated only when two conditions are met; i.e., when the change rate of pressure at the inlet is below a first predetermined value, and when the pressure at the inlet side is above a second predetermined value. Therefore, during operation attended by frequent acceleration and deceleration experienced in hilly terrain, the combustion state in the engines deteriorates resulting in an increase in exhaust gases and operation of the regeneration combustor is intermittent. Accordingly, the particulate filter cannot be regenerated properly and becomes clogged.
The object of the present invention, therefore, is to provide an improved system for regenerating a particulate filter in a Diesel engine.